A large number of various locking devices for releasably locking an inner element to an outer tube in various axial positions relative to each other are already known. In principle, these are used in two different areas. These are: stands and supports for taking up principally axial forces; and, tool shafts for taking up not only axial and lateral forces, but also torque. Examples from the first category include furniture legs, various types of sticks, microphone stands, camera stands, ski poles, etc. Examples from the second include shafts for gardening, painting shafts, cleaning shafts, etc.
Functionally, a division can be made into shape-dependent locks and friction-dependent locks. Shape-dependent locks have fixed positions that can be created using holes or transverse slots into which corresponding locking pins can be inserted—see, for example, GB1532723 or WO2005/087329. This type of lock has few parts and may provide a reliable locking function. However, it has the disadvantage that it only allows distinct locking positions. As regards friction-dependent locks, these have the advantage of offering freely selectable locking positions, but the disadvantage that it is more difficult to achieve a reliable locking function using this type of lock. Amongst a large number of different documents, WO2004/090349 can here be mentioned.
A further division can be made on the basis of the locking member's location in relation to the most common main structures, i.e. an outer tube and a therein displaceable inner tube. The locking member can here be: 1) on the end of the inner tube that is inserted in the outer tube—working against the outer tube's inner mantle surface, or 2) on the outer tube's end—working against the inner tube's outer mantle surface, or 3) on the end of an internal tube that is joined to an outer tube inserted into the inner tube—working against the inner mantle surface—see, for example, WO2005/108015.
Yet another division can be made on the basis of the location of the operating member, the most widespread of the locking members here being located on one end of the inner tube and operated by turning the inner and outer tubes relative to each other.
Another known operating principle for a locking member located on one end of the inner tube is to use a non-circular torsion rod that emerges from the outer tube's free end. The locking member has a through-hole for the torsion rod and can thus be displaced axially relative to this. The locking member can be actuated by turning the torsion rod via a rotary knob on the outer tube's free end. US2006/0282988, U.S. Pat. No. 6,361,002, U.S. Pat. No. 6,862,776 and GB2423275 can here be mentioned amongst the more recent documents. All the devices described in these documents use locking bodies that, acted on by the rotary movement, are pressed in a radial direction against the outer tube's inner mantle surface.
As regards tool shafts, it is most usual for the outer tube to point upwards, thereby giving the operator an unbroken gripping surface and a low moment of inertia in respect of sideways movements. Here, it is especially favourable to have an operating member located close to the upper end of the outer tube. The operator does not then have to bend when adjusting shaft length. Examples of such devices are EP1313956 (where the operating member actuates a locking member on the lower end of the outer tube) and WO2005/000305 (where several described designs include a locking member working against the inner tube's inner mantle surface, the locking member being on the lower end of a tube emerging from the upper end of the outer tube). A locking member as per FIGS. 44-49 can be mentioned in particular here. This has a tubular locking sleeve slotted by a longitudinal slot in the form of a wedge-shaped cut-out. Two axially opposed wedges work in a tangential direction in this slot. Operated by small forces exerted via a spring-loaded push rod, this locking member is self-locking in both directions without having to employ special friction materials. Irrespective of this, it is easy to release (provided that the shaft is not axially loaded). The locking device thereby demonstrates considerable advantages over the majority of other friction-dependent locking devices. The latter are unsuitable for demanding applications. This is because of insufficient locking forces despite large operating forces. These latter make it extremely difficult to offer an easy-to-use and reliable operating function. However, the locking device described in WO2005/000305 suffers from disadvantages in the form of an extra inner tube and complicated assembly. It can also be mentioned that the lock is of the disconnection type. Of course, this is excellent as regards operation but, for it to take up a spontaneously locked position, requires the engagement of a spring. A further disadvantage is that the operating member does not have full control over the lock—it cannot be disconnected when the shaft is axially loaded.